Fgn. Cloke et al., MOLECULAR AND ELECTRONIC-STRUCTURES OF BIS[1,4-BIS(TRIMETHYL-SILYL)CYCLOOCTATETRAENE] SANDWICH COMPLEXES OF TITANIUM AND ZIRCONIUM, Journal of the Chemical Society. Dalton transactions, (19), 1994, pp. 2867-2874
The reaction between 2 equivalents of [Li2{C8H6(SiMe3)2}] and [MCl4(th
f)2] (M = Ti or Zr) in tetrahydrofuran (thf) afforded the sandwich com
plexes [M{C8H6(SiMe3)2}2]. X-Ray studies showed that the zirconium com
pound adopts a structure in which one ring is bound in an eta8 fashion
whilst the other adopts a novel eta3 co-ordination mode. This unusual
bonding situation has been studied using extended-Huckel molecular-or
bital calculations and photoelectron spectroscopy. In contrast, the ti
tanium compound adopts a solid-state structure in which one ring is et
a8 bound and the other is less readily classified, being intermediate
between the eta3 structure found for Zr and the eta4 structure found i
n [Ti(C8H8)2]. Variable-temperature solution NMR studies on [M{C8H6(Si
Me3)2}2] showed that the two rings remain indistinguishable even at 19
3 K for M = Zr, whereas for M = Ti the two rings only become equivalen
t on the NMR time-scale above 328 K.